1. Field of the Invention
The invention concerns a wireless telephone service access method, the service being provided by a network essentially comprising: fixed stations; wireless digital telephones linked by radio to the fixed stations; and an integrated services digital public switched telephone network. The invention is more particularly concerned with a wireless telephone service provided by an "intelligent" network to be described later.
2. Description of the Prior Art
A conventional wireless telephone service access method has two functions: to verify that the calling party is entitled to use the telephone that he is using; and to verify that the telephone is covered by a valid subscription including the entitlement to use the wireless telephone service. For the first of these checks the caller enters a confidential code (or personal identification number PIN) using the telephone keypad. This is compared with the code stored in the telephone to enable the telephone if they are identical. The second verification, or caller authentication, is more difficult as the subscriber characteristics of all service subscribers constitute a large volume of information which is constantly changing. In particular, a subscription is anulled if a telephone is lost or stolen.
In a known wireless telephone service access method the caller is authenticated by transmitting from the telephone to the fixed station a number identifying the subscriber. Each fixed station has its own authentication system which includes a blacklist of anulled subscriptions. Each fixed station is connected to the public switched telephone network by telephone channels only. Data for updating the blacklist is transmitted over these telephone channels during off-peak times using a modem.
This authentication method is not particularly secure, as the blacklist is updated only once a day in the best possible case; and also because the subscription number can be intercepted by a third party during the radio transmission.
What is more, this known method makes no provision for offering different types of subscription including authorization or rejection of access on the basis of the called number or on the basis of the subscriber account debit. Nor does it have any provision for transmitting to the caller's telephone a message to indicate the account debit on a display in the telephone. These are serious drawbacks with respect to the renting out of wireless telephones as the renter cannot restrict the rights provided by a subscription, to protect himself against unpaid bills, by barring certain numbers or by setting a ceiling on the subscriber account debit; and also because it is not feasible to apply a ceiling to a renter account debit without the renter being advised of the account status before each call.
An object of the invention is to propose an access method which offers increased protection against fraudulent misuse and which also makes provision for: selective authorization of certain numbers; sending to the caller's telephone a message indicating the account debit; and selectively authorizing a call according to the subscriber account status. This object is achieved by using an intelligent network structure for the wireless telephone network and by implementing the access method as will now be defined.